The present invention is related to wireless networks, and in particular to determining the location of wireless stations in a wireless network.
Use of wireless networks such as wireless local area networks (WLANs) is becoming widespread. Locating radios in a wireless communication system such as a WLAN enables new and enhanced features, such as location-based services and location-aware management. Location-based services include, for example, assigning the correct, e.g., closest printer to a wireless station of a WLAN.
A WLAN may be ad hoc, in that any station may communicate directly with any other station, or have an infrastructure in which a station (called a “client station” or simply a “client”) can only communicate via an access point (AP)—a station that acts as a base station for a set of clients. The access point is typically coupled to other networks that may be wired or wireless, e.g., to the Internet or to an intranet. That wider network is called the “wired” network herein, and it is to be understood that this wired network may be an internetwork that includes other wireless networks.
WLAN management applications of radiolocation include the location of client stations and the location of rogue access points. See for example, concurrently filed incorporated-by-reference U.S. Provisional Patent application Ser. No. 60/490,847 titled “A METHOD, APPARATUS, AND SOFTWARE PRODUCT FOR DETECTING ROGUE ACCESS POINTS IN A WIRELESS NETWORK” to inventors Olson, et al., for more details of the latter application and how radiolocation may be used to aid rogue access point detection.
A number of techniques have been proposed for radiolocation. Prior art methods are known that rely on the Global Positioning System (GPS). GPS, however, is known to have poor indoor reception and long acquisition time. GPS also requires additional GPS hardware in the wireless station that would increase the cost of stations, e.g., client devices.
Prior art methods also are known that rely on time difference of arrival (TDOA) estimation. Such methods require relatively precise time synchronization at each station, which in turn requires non-standard hardware that differs from that in today's WLAN stations, e.g., stations that conform to the IEEE 802.11 standard.
Prior art methods also are known for WLANs that use signal strength measurements using existing mobile station hardware. Such methods, however, require training that in turn requires taking time-consuming signal strength measurements at numerous locations by a cooperative mobile client station.
A prior art method also is known for WLANs that uses RF modeling. The modeling, however, requires detailed input of building layout, wall location, and construction materials.
Thus, there is a need for a method for radiolocation using available signal strength measurements at wireless stations that does need additional hardware in addition to regular radio hardware, and that requires relatively little training. There further is a need for a radiolocation method wherein the training can be accomplished automatically by each infrastructure access point.